Catholic Easter calculation using Julian Day Numbers (JDN) & Gauss modular mathematics is a streamlined method that determines the date of Easter Sunday (Paschal Sunday) in the proleptic Gregorian calendar by anchoring to the ecclesiastical equinox of March...
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Catholic Easter calculation using Julian Day Numbers (JDN) & Gauss modular mathematics is a streamlined method that determines the date of Easter Sunday (Paschal Sunday) in the proleptic Gregorian calendar by anchoring to the ecclesiastical equinox of March 21.
The process begins by computing the Epact (the age of the moon on March 21) via a modular formula involving the year: MOD(19*MOD(Year,19) + floor(Year/100) - floor(floor(Year/100)/4) - floor((floor(Year/100) - floor((floor(Year/100)+8)/25)+1)/3) +15, 30). This is added to the JDN of March 21 (computed with a formula incorporating year adjustments for the Julian/Gregorian transition) to obtain the JDN of the Paschal Full Moon. The day-of-week offset is then derived using modular arithmetic on the JDN, allowing calculation of the subsequent Sunday (Easter) by skipping forward the appropriate number of days. Finally, the difference in days from March 21 is used to express the result as either a March or April date. Examples includ
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